Interpretive Summary: Beneficial insects, such as predators, mass reared by commercial insectaries to release for biological control must be of high quality to maximize their effectiveness against pest insects. Predators reared on the more economically produced artificial diet formulations may not have the best amounts of vitamins and minerals for optimum production. Vitamin C is required by insects for a variety of life processes such as resistance to infections, egg production and general growth and survival. This study illustrated the benefits and drawbacks of dietary vitamin C levels on the beneficial predatory insect, the spined soldier bug mass reared on artificial diets. We fed spined soldier bugs a range of vitamin C concentrations and found the one narrow range of dietary concentration of vitamin C that yielded the best egg production, growth rate and survival over two generations. Levels of vitamin C on either side of this best concentration resulted in slower growth, lower survival and less egg production. Two generations of growth on vitamin C concentrations too low or too high increased the negative effects. The outcome of this study will assist researchers and insectaries in the mass rearing of high quality beneficial insects by optimizing dietary levels of vitamin C. Together, our results indicate that biofortification of food crops with vitamin C can have unpredictable downstream impacts on the range of pest insects and the efficacy of pest insect control with beneficial predatory insects.

Technical Abstract:
We report here the effects of ascorbic acid concentrations (0.07, 0.3, 3.0 and 30.0 g/L) in artificial diets on growth rates, adult weights, fecundity and survival of the predatory stink bug, Podisus maculiventris. Overall, a dietary level of 3.0 g/L gave the shortest developmental times over both generations. The likelihood of egg hatch at one ascorbic acid concentration compared to another concentration suggested that egg hatch increased as the concentration of ascorbic acid increased from 0.07 g/L to 3.0 g/L and then declined from 3.0 g/L to 30 g/L. The combination of the maximum egg oviposition at 0.3 g/L and 3.0 g/L, egg hatch at 3.0 g/L and survival at 0.07 and 0.3 g/L suggest an overall superior performance at a concentration between 0.3 and 3.0 g/L. Additionally, it suggests there is a correlation between more eggs laid at the lower levels of ascorbic acid concentration until a critical level is reached between 0.3 and 3.0 g/L. Depletion of ascorbic acid below 3.0 g/L or addition of ascorbic acid above 3.0 g/L lowered the likelihood of egg hatch, which became more pronounced in the second generation. This is consistent with previously published information for phytophagous insects. We also found increased survival and evidence for bioaccumulation with increased dietary ascorbic acid concentration. Collectively, these results suggest there may be a level of biofortification in crops that could be passed upwards to higher trophic levels and cause a complex response by predatory insects.